The term “LIDAR” refers to a technique for measuring distances of visible surfaces by emitting light and measuring properties of the reflections of the light. The term is a combination of parts of the words “light” and “radar,” although the term is often thought of as an acronym for “Light Detection and Ranging.”
A LIDAR system typically has at least one laser emitter and a corresponding sensor element. The laser emitter may comprise a laser such as an injection laser diode (ILD) that directs light in the direction of an object or surface. The sensor element may comprise a photodetector such as a photomultiplier or avalanche photodiode (APD) that converts light intensity to a corresponding electrical signal. Optical elements such as lenses may be used in the light transmission and reception paths to focus and direct light.
A LIDAR system has signal processing components that analyze reflected light signals to determine the distances to surfaces from which the emitted laser light has been reflected. For example, the system may measure the propagation time of a light signal as it travels from the laser emitter, to the surface, and back to the sensor element. A distance is then calculated based on the flight time and the known speed of light.
Some LIDAR devices can measure the distances of multiple surface points within a scene. For each surface point, the LIDAR system can determine both the distance of the surface point and its angular direction with respect to the device. This capability can be used to create a point cloud comprising three-dimensional coordinates of the multiple surface points.
To measure coordinates of multiple surface points, a LIDAR system may use multiple laser emitters and/or multiple sensor elements. Alternatively, a LIDAR system may physically move one or more lasers and/or detectors to scan over a scene while repeatedly taking measurements of different surface points.
LIDAR systems have been used to inform guidance, navigation, and control systems in autonomous vehicles. In systems such as this, one or more LIDAR devices are configured to produce a surface map indicating the 3D coordinates of visible surface points surrounding the vehicle. A guidance, navigation, and control system analyzes this data to identify obstacles, to perform obstacle avoidance, and to determine a desired path of travel.